Solar chimney

A solar chimney – is referred to as a thermal chimney – a way of improving the natural ventilation of buildings by using convection of air heated by passive solar energy . A simple description of a solar chimney is that of a vertical shaft utilizing solar energy to enhance the natural stack ventilation through a building.

The solar chimney has been used for centuries, particularly in the Middle East and Near East by the Persians , as well as in Europe by the Romans .

Description

In its simplest form, the solar chimney consists of a black-painted chimney . During the day solar energy heats the chimney and the air within it, creating an updraft of air in the chimney. The suction created at the chimney’s base can be used to ventilate and cool the building below. [1] In most parts of the world it is easier to harness wind power for such ventilation as a windcatcher , but it can not be avoided.

There are, however, a number of solar chimney variations. The basic design elements of a solar chimney are:

The solar collector area: This can be located in the top part of the chimney or can include the entire shaft. The orientation, type of glazing, insulation and thermal properties of this element are crucial for harnessing, retaining and utilizing solar gains.

The main ventilation shaft: The location, height, cross section and the thermal properties of this structure are also very important.

The sizes of the air inlet and outlet are also significant.

A principle has-beens Proposed for solar power generation, using a wide greenhouse at the base Rather than Relying Solely is heating the chimney Itself. (For further information on this issue, see Solar updraft tower .)

Solar chimneys are painted black so they absorb the sun’s heat more effectively. When the air inside the chimney is heated, it rises and pulls cold air through the heat exchange tubes.

Solar chimney and sustainable architecture

Solar chimneys, also called heat chimneys or heat stacks, can also be used to reduce the energy used by mechanical systems. Air conditioning and mechanical ventilation has been used for many years, especially offices, in developed countries. Pollution and reallocating energy supplies. Innovative technologies along with bioclimatic principles and traditional design strategies are often combined to create new and successful design solutions. The solar chimney is one of these concepts, mostly through research and experimentation.

Solar chimney can serve many purposes. Direct gain warms air inside the chimney causes it to rise out of the air. This drawing of air can be used to ventilate a home or office, to draw a geothermal heat exchange, or to ventilate a specific area such as a composting toilet.

Natural ventilation can be created by providing ventilation in the upper level of a convection and escape to the outside. At the same time, air can be drawn in the wind at the lower level. Trees may be planted on that side of the building to provide shade for cooler outside air.

This natural ventilation process can be enhanced by a solar chimney. The chimney has to be higher than the roof level, and has to be constructed on the wall facing the direction of the sun. Absorption of heat from the sun can be increased by using a glazed surface on the side facing the sun. Heat absorbing material can be used on the opposite side. The size of the heat-absorbing surface is more important than the diameter of the chimney. A large surface area allows for more effective heat exchange with the necessary air for heating by solar radiation. Heating of the air within the chimney will enhance convection, and hence airflow through the chimney. Openings of the winds in the chimney should face away from the direction of the prevailing wind .

To further Top maximize the cooling effect, the incoming air May be led through underground ducts before it is allowed to enter the building. The solar chimney can be improved by integrating it with a trombe wall . The added advantage of this design is that the system can be used during the cold season, providing solar heating instead.

A variation of the solar chimney concept is the solar attic . In a hot sunny climate attic space is often blazingly hot in the summer. In this case, there is a need for increased air conditioning . By integrating the attic space with a solar chimney, the hot air in the attic can be put to work. It can help the convection in the chimney, improving ventilation. [4]

The use of a solar chimney can be used in general , and CO 2 emissions and pollution in general. Potential benefits regarding natural ventilation and use of solar chimneys are:

improved ventilation rates on still, hot days

reduced reliance on wind

improved control of airflow

greater choice of air intake (ie leeward side of building)

improved air quality and noise levels in urban areas

increased night time ventilation rates

ventilation of narrow, small spaces

Potential benefits regarding passive cooling may include:

passive cooling during warm season (mostly on still, hot days)

improved night cooling rates

enhanced performance of thermal mass (cooling, cool storage)

improved thermal comfort (improved air flow control, reduced drafts)

Precedent Study: The Environmental Building

The Building Research Establishment (BRE) office building in Garston, Watford, United Kingdom, incorporates solar-assisted passive ventilation stacks as part of its ventilation strategy.

Designed by architects Feilden Clegg Bradley, the BRE offices aim to Reduce energy consumption and CO 2 emission by 30% from current best practice guidelines and sustain comfortable environmental requirements without the use of air conditioning. The passive ventilation stacks, solar shading, and hollow concrete slabs. Ventilation and heating systems are controlled by the building management system (BMS) while a degree of user override is provided to adjust conditions to occupants’ needs.

The building utilizes five vertical shafts as an integral part of the ventilation and cooling strategy. The main components of these stacks are a south-facing glass-block wall, thermal mass walls and stainless steel round exhausts rising to a few meters above roof level. The chimneys are connected to the curved hollow concrete floor slabs which are cooled via night ventilation. Pipes embedded in the floor can provide additional cooling utilizing groundwater.

On warm windy days are drawn in through the curved hollow concrete floor slabs. Stack ventilation naturally rising out of the steel chimneys enhances the air flow through the building. The movement of air across the chimney tops enhances the stack effect. During warm, still days, the building relies mostly on the stack effect while being taken from the shady north side of the building. Low-energy fans in the tops of the stacks can also be used to improve airflow.

Overnight, control systems enable ventilation paths through the hollow concrete slab removing the heat stored during the day, which then remains cold for the following day. Gives The exposed curved ceiling area more area than a flat ceiling Would, acting as a heat sink , again providing good summer cooling. The results of this study show that they can be used to improve their thermal energy efficiency. [5]

Passive down-draft cool tower

A technology closely related to the solar chimney is the evaporative down-draft cooltower. In areas with a hot, arid climate this approach contribuer May to a sustainable way to Provide air conditioning for buildings.

Evidence of moisture from the pads on the top of the Togonites built by the Dogon people of Mali, Africa contributes to the coolness felt by the men who rest underneath. The women’s buildings on the outskirts of the city are functional.

The principle is to allow water to evaporate at the top of a tower, using evaporative cooling pads or by spraying water. Evaporation cools the incoming air, causing a downdraft of cool air that will bring the temperature inside the building. [6] Airflow can be increased by using a solar chimney on the opposite side of the building to help in hot air to the outside. [7] This concept has been used for the Visitor Center of Zion National Park . The Visitor Center was designed by the High Performance Buildings Research of the National Renewable Energy Laboratory (NREL).

The principle of the downdraft cooltower has been proposed for solar power generation. See Energy Tower for more information.